The present invention relates to an electronic fuse. In particular, the present invention relates to an electronic circuit which will act as an electronic fuse for a power semiconductor device in the event of excessive current through the semiconductor device.
U.S. Pat. No. 6,356,423 to Hastings et al. discloses a solid state protection circuit for electrical apparatus in which electrical equipment is safeguarded from damage due to faults by a circuit that provides several levels of protection. A semiconductor switch and a current sensor are placed in series with the electrical equipment. In a first mode of operation when the magnitude of current is less than a first threshold, the semiconductor switch is maintained in a continuous conductive state. In the second mode of operation when the magnitude of current is greater than the first threshold and less than a second threshold, the semiconductor switch is rendered non-conductive after a predefined period of time. In the third mode of operation when the magnitude of the current is greater than the second threshold, the semiconductor switch is alternately pulsed conductive and non-conductive to limit the current to the load to less than the second threshold. The circuit described also has a fourth mode of operation when the magnitude of current is greater than a third threshold that is greater than the second threshold whereby the semiconductor switch is rendered non-conductive until the apparatus is specifically reset.
In certain instances, the above described prior art device is inadequate. In particular, there are conditions wherein the pulsed mode of operation occurs where the semiconductor device may be damaged. The above described prior art device limits the amount of time in which the semiconductor device can be pulsed by counting the number of pulses. If the pulse count exceeds a predetermined count, the semiconductor device is rendered nonconductive.
However, the prior art device fails to address a circumstance where the pulsed mode does not exceed the predetermined count, and the semiconductor device again enters the continuous mode of operation and thereafter enters the pulsed mode again. It is not clear if the prior art circuit will trip the semiconductor device when the pulse count exceeds the predetermined pulse count or the pulse count starts anew upon the re-entry into the pulsed mode. In certain circumstances, it may not be desirable to trip the semiconductor device. Further, it may also be described to turn off the semiconductor device even through the pulse count has not been exceeded, but where the pulsed mode of operation is requested with insufficient duration between the requests for pulsed mode operation.
Accordingly, there is a need for an improved electronic fuse circuit that will appropriately protect the semiconductor switching device in the event of interrupted pulsed mode operation.